Coat an 8-inch square baking dish with cooking spray and set aside.

Place the Marshmallow Creme, butter, and cocoa in a large, heavy saucepan. Cook over medium heat, stirring with a heatproof spatula until the mixture is mostly melted. When just a few lumps of Marshmallow Creme remain, remove the pot from the heat and stir until the mixture is smooth. Dump in the cereal and mix until it is well coated. Spread the cereal mixture in the prepared pan and press it into an even layer. Moisten your hand lightly with water and press to pack it very firmly.

Melt the chocolate in a small bowl in the microwave. Using a fork, drizzle the melted chocolate over the pan in long lines. Refrigerate, uncovered, until it sets, about 2 hours.

Run a knife around the edge of the pan. Use the blade to help lift the packed cereal out of the pan. On a cutting board, use a sharp knife to cut Cocoa Crisp into 16 squares. Serve immediately, or refrigerate on a plate, covered with foil, for up to 2 days.